Behaviour of cold-formed steel tensile members strengthened with GFRP using different techniques

Cold-formed steel (CFS) members may need strengthening for a multitude of reasons such as their intrinsic weakness to fail locally before the design load is reached, deterioration due to corrosion or modification in the design standards. Fibre-reinforced polymers such as glass-fiber-reinforced polymers (GFRP) have been increasingly used for strengthening deficient steel structures. GFRP is usually employed as wet-laid laminates or as pultruded plates. The present work is a laboratory and finite element study for comparing the effectiveness of GFRP wet-laid laminates and pultruded plates as reinforcement elements for thin CFS members. A total of 10 specimens were tested in laboratory under tension. Two different reinforcement lengths (i.e., along the entire steel member and other being a central reinforcement patch) were studied for steel members strengthened with fabric laminates and pultruded plates. It was observed that CFS members reinforced with GFRP plates and GFRP laminates exhibited different failure modes. While the dominant mode of failure in the wet-laid laminates was debonding, steel yielding was observed in specimens reinforced with pultruded plates. Also, a 34% increase in the strength was observed in the specimens where pultruded plates were used and about 16.85% in the specimens where laminates were used for strengthening. This indicates that GFRP pultruded plates performed better in reinforcing thin CFS members. It was also found that reinforcing the entire length of the steel member could increase the effectiveness of the strengthening technique significantly. A finite element model was simulated and validated against the experimental results. The validated finite element model was then employed to study the effect of key parameters affecting the economy of the strengthening technique. It was observed that the thickness of GFRP can be optimized, and for the present study, a GFRP thickness of 6 mm was found to be optimum.